1. Field of the Invention
This invention relates to a tank for use with an electric equipment, such as a transformer or a reactor of large capacity, and more particularly to a tank for use with an electric equipment, which is composed of at least upper and lower parts, with its parting line running in the horizontal direction.
2. Description of the Prior Art
Recently, transmission and distribution voltages have been raised to ultra-high levels of as much as 500 KV, while the capacity of the power transformer is increased to the order of 1000 MVA, so that the size of electric equipment for use in a power transmission or distribution system, such as for instance, a transformer, is increased to a great extent. For simplicity of description, a transformer will be referred to herein as an example of one application of the present invention.
With a transformer having a large capacity of, for example, 500 KV, a tank which houses therein the iron core and windings of the transformer is composed of an upper part 1 and a lower part 2, as shown in FIG. 1. Pairs of vertical reinforcing stays 5, 6 on the upper and lower parts of the tank align with each other in the vertical direction and are secured to the outer surfaces of the upper and lower parts 1, 2 of the tank, respectively. The upper and lower parts 1, 2 are formed with interconnecting flanges 3, 4, respectively, so that the vertical reinforcing stays 5, 6 are discontinued in the position of the interconnecting flanges 3, 4, when mated with each other. This in turn causes a decrease in the mechanical strength of the reinforcing stays 5, 6 in the aforesaid position, when the tank is subjected to internal and external pressures. To avoid this, the respective paired stays 5, 6 are coupled to each other by means of reinforcing interconnecting members 7 and bolts 8.
However, such an arrangement suffers from shortcomings in that the aforesaid bolts 8 only serve as anchors for the reinforcing interconnecting member which is subjected to an elastic deformation due to a bending moment created by an internal pressure or an external pressure, and that the interconnecting flanges 3, 4 provide pin joints for the bending moment, in their appearance.
This will be described in more detail with reference to FIGS. 1 to 4, hereunder.
When uniformly distributed external pressure W acts on a tank composed of an upper part 1 and a lower part 2 which are coupled to each other by means of interconnecting flanges 3, 4, the distribution of bending moments is such that, as shown in FIG. 4 (B), the bending moment is nullified in the position of the interconnecting flanges 3, 4, while the bending moments M are increased at points spaced increasingly from the flanges 3, 4 in the vertical direction, peaking on the corners of the upper and lower parts 1, 2 of the tank. A noticeable stress concentration takes place on th corners of the upper and lower parts 1, 2 of the tank, because of the addition of the bending moments in the widthwise direction. Thus, the vertical reinforcing stays 5, 6 fail to achieve their functions to reinforce the mechanical strength of the tank to satisfaction, with the accompanying failure to provide rigid and strong joints for the interconnecting flanges.
The aforesaid bending moments will be described in more detail hereunder. As shown in FIG. 3, the vertical reinforcing stays 5, 6, which are secured to the upper and lower parts l, 2 of the tank, are completely discontinued because of the presence of interconnecting flanges 3, 4 so that the stays 5, 6 are coupled to each other by means of the reinforcing interconnecting members 7 which are attached to the outer surfaces of the stays 5, 6. Accordingly, in case an external pressure is exerted on the tank, the outer walls of the respective vertical reinforcing stays 5, 6 are subjected to a compression due to bending moments, as shown by arrows (solid lines), while the inner walls of the stays 5, 6 (on the side of the tank) are subjected to a tension, as shown by arrows (dotted lines), and in addition the center portions of the stays are subjected to a shear force. Meanwhile, since the reinforcing interconnecting members 7 are attached to the outer surfaces or walls of the vertical reinforcing stays 5, 6 and are secured thereto by means of bolts 8, the transmissions of the compression and tension forces are effected only through the inner walls of the reinforcing interconnecting members 7 i.e., through the walls of the members 7 on the side of the tank, while a shear force is transmitted through part of the reinforcing interconnecting members (bolts 8), due to the absence of members for transmitting the shear force. This approximates the so-called pin-joint As a result, the bending moments are greatly increased on the corners of the upper and lower parts of the tank, as shown in FIG. 4 (B).
To avoid this, there has been proposed a tank contruction in which the interconnecting flanges of the upper and lower parts of the tank are made as a complete rigid joint i.e., as an integral body. This provides an advantage in that the distribution of the bending moments exhibits quadratic characteristics which are continuous in both widthwise and lengthwise directions of the tank, as shown in FIG. 5 (B), thus eliminating the concentration of the bending moments on the corners of the tank, and as a result, for achieving a desired mechanical strength of the prior art tank, the joints of the intermediate flange portions should be rigid. However, this attempt at solution to the problem suffers from a shortcoming in that the rigidity of the interconnecting flanges is lower than that of the reinforcing interconnecting members adapted to interconnect the vertical reinforcing stays. For this reason, to increase the rigidity and mechanical strength of the joints between the upper and lower parts of the tank, it is imperative that the sizes of the reinforcing interconnecting members as well as the interconnecting flanges be increased to an extent more than required, and that, in the worst case, the thicknesses of steel plates used in the tank must be increased, thus raising the manufacturing cost of the tank.